Soil Survey Manual - USDA

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Soil Survey Manual
Soil Science Division Staff
Agriculture Handbook No. 18
Soil Survey Manual
By Soil Science Division Staff
United States Department of Agriculture
Handbook No. 18
Issued March 2017
This manual is a revision and enlargement of 
U.S. Department of Agriculture Handbook No. 
18, the Soil Survey Manual, previously issued 
October 1962 and October 1993. This version 
supersedes both previous versions.
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i
Table of Contents
List of Figures ................................................................................vii
List of Tables .................................................................................xvii
Introduction to the Fourth Edition ......................................xxiii
Purpose ........................................................................................xxiii
Need for Additions and Revisions ................................................ xxv
Online Access .............................................................................xxvii
Citation and Authorship ..............................................................xxvii
Acknowledgements ...................................................................xxviii
References .................................................................................xxviii
Chapter 1.—Soil and Soil Survey ............................................. 1
Soil Survey—Definition and Description ......................................... 1
Early Concepts of Soil ...................................................................... 3
Early Development of Soil Classification ........................................ 7
Modern Concept of Soil ................................................................... 8
Development of Soil Taxonomy ....................................................... 9
Scientific Foundation of Soil Survey .............................................. 10
Development of the Soil Survey in the U.S. .................................. 13
References ...................................................................................... 18
Chapter 2.—Landscapes, Geomorphology, and Site 
Description ................................................................................ 21
Introduction .................................................................................... 21
Capturing Soil-Landscape Relationships at Various Scales ........... 25
Placing Soil-Landscape Relationships in Their Proper Context .... 28
Consistently Describing Landscapes, Landforms, and 
Geomorphology ....................................................................... 30
Parent Material ............................................................................... 53
Bedrock .......................................................................................... 66
Lithostratigraphic Units .................................................................. 69
Erosion ............................................................................................ 70
ii Table of ConTenTs
Land Cover ..................................................................................... 77
Vegetation ....................................................................................... 78
Ecological Sites .............................................................................. 79
Integrated Natural Resource Inventories ........................................ 80
References ...................................................................................... 80
Chapter 3.—Examination and Description of Soil 
Profiles ........................................................................................ 83
Introduction .................................................................................... 83
General Terms Used to Describe Soils ........................................... 84
Studying Pedons ............................................................................. 87
Designations for Horizons and Layers ........................................... 91
Near Surface Subzones ................................................................. 114
Root-Restricting Depth ................................................................. 118
Particle-Size Distribution ............................................................. 119
Soil Texture .................................................................................. 120
Rock Fragments and Pararock Fragments .................................... 131
Artifacts ........................................................................................ 137
Compound Texture Modifiers ....................................................... 140
Fragments on the Surface ............................................................. 141
Soil Color ..................................................................................... 145
Soil Structure ................................................................................ 155
Internal Ped and Void Surface Features ........................................ 163
Concentrations .............................................................................. 168
Pedogenic Carbonates ................................................................. 173
Redoximorphic Features ............................................................... 177
Consistence ................................................................................... 180
Roots ............................................................................................. 193
Pores ............................................................................................. 195
Animals ........................................................................................ 197
Selected Chemical Properties ....................................................... 198
Soil Water ..................................................................................... 205
Soil Temperature ..........................................................................228
References .................................................................................... 230
Chapter 4.—Soil Mapping Concepts ................................... 235
Soil Mapping Process ................................................................... 235
Field Operation and Equipment ................................................... 241
 soil survey Manual iii
Soil Identification and Classification ............................................ 245
Soil Map Units .............................................................................. 248
Kinds of Map Units ...................................................................... 256
Minor Components Within Map Units ......................................... 260
Designing and Documenting Map Units ...................................... 262
Naming Map Units ....................................................................... 265
Orders of Soil Surveys ................................................................. 268
Correlation Steps .......................................................................... 276
Quality Control and Quality Assurance ........................................ 280
Records and Documentation ........................................................ 281
Soil Handbook .............................................................................. 284
Soil Maps Made by Other Methods ............................................. 289
Supporting Data ............................................................................ 291
References .................................................................................... 292
Chapter 5.—Digital Soil Mapping ......................................... 295
Principles and Concepts ............................................................... 295
Stages and Processes .................................................................... 299
Applications of Digital Soil Mapping .......................................... 341
Summary ...................................................................................... 346
References .................................................................................... 346
Chapter 6.—Tools for Proximal Soil Sensing ................. 355
Introduction .................................................................................. 355
Common Geophysical Methods ................................................... 356
Less Common Proximal Sensing Methods .................................. 376
References .................................................................................... 387
Chapter 7.—Soil Survey Data Collection, 
Management, and Dissemination .................................. 395
Introduction .................................................................................. 395
Automated Data Processing in Soil Survey ................................. 396
Recording Data and Information—Field and Lab ........................ 400
Soil Information Systems ............................................................. 415
History of Soil Data Management in the U.S. .............................. 421
References .................................................................................... 432
Chapter 8.—Interpretations: The Impact of Soil 
Properties on Land Use ..................................................... 433
Introduction .................................................................................. 433
iv Table of ConTenTs
Interpretive Models ...................................................................... 436
Current U.S. Interpretive System ................................................. 440
Map Units and Soil Interpretations .............................................. 446
Interpretive Soil Properties ........................................................... 449
Dynamic Soil Properties ............................................................... 456
Interpretive Applications .............................................................. 457
Areal Application of Interpretations ............................................. 475
References .................................................................................... 478
Chapter 9.—Assessing Dynamic Soil Properties 
and Soil Change .................................................................... 481
Importance of DSPs ...................................................................... 481
How to Collect DSPs for Soil Survey .......................................... 483
Data Collection Plan ..................................................................... 489
Analyzing Dynamic Soil Property Data ....................................... 497
Summary of DSPs in Soil Survey ................................................ 501
References .................................................................................... 502
Chapter 10.—Subaqueous Soil Survey ............................. 505
Introduction .................................................................................. 505
Sampling, Description, Characterization, and Classification ....... 506
Soil-Landscape Relationships ...................................................... 513
Survey Methods and Procedures .................................................. 516
Significance of Subaqueous Soil Information .............................. 519
References .................................................................................... 521
Chapter 11.—Human-Altered and Human- 
Transported Soils ................................................................. 525
Introduction .................................................................................. 525
Background .................................................................................. 526
Importance .................................................................................... 531
Occurrence .................................................................................... 532
Identification ................................................................................. 532
Description ................................................................................... 536
Survey Methods and Procedures .................................................. 537
Pedon Descriptions ....................................................................... 549
References .................................................................................... 552
Appendix 1.—Official Soil Series Description ................ 555
Olton Series .................................................................................. 555
 soil survey Manual v
Appendix 2.—Detailed Map Unit Description .................. 561
OcA—Olton clay loam, 0 to 1 percent slopes .............................. 561
Appendix 3.—NCSS Soil Characterization 
Database ................................................................................... 563
Appendix 4.—Web Soil Survey ............................................. 573
Soil Survey Maps and Map Products ........................................... 573
Index ................................................................................................. 587
vii
List of Figures
Chapter 1.— Soil and Soil Survey
No figures.
Chapter 2.—Landscapes, Geomorphology, and Site 
Description
Figure 2-1 ....................................................................................... 23
A talus cone in a canyon illustrating a distinct, sharp break between 
landforms.
Figure 2-2 ....................................................................................... 26
A scarp slope of a cuesta above an alluvial flat. 
Figure 2-3 ....................................................................................... 27
Diagram of the change of dominant surface fragment sizes and 
percentages along a transect of a scarp slope on a cuesta. 
Figure 2-4 .......................................................................................27
A comparison of digital maps with 60 x 60 m and 10 x 10 m grid 
sizes. 
Figure 2-5 ....................................................................................... 28
Images showing changes in slope class interpretation as affected by 
DEM resolution from LiDAR. 
Figure 2-6 ....................................................................................... 32
A canyonlands landscape in the San Rafael Swell, Utah.
Figure 2-7 ....................................................................................... 33
Loess hill and river valley landforms in western Iowa, along the 
Missouri River.
Figure 2-8 ....................................................................................... 34
Turf hummock microfeatures in a wet meadow in Oregon.
Figure 2-9 ....................................................................................... 39
A quarry as an example of an anthropogenic landform.
Figure 2-10 ..................................................................................... 40
Soil conservation terraces as an example of an anthropogenic 
microfeature.
Figure 2-11 ..................................................................................... 41
Effect of slope aspect on vegetation and tree seedling survival. 
viii lisT of figures
Figure 2-12 ..................................................................................... 42
Simple versus complex slopes and slope positions. 
Figure 2-13 ..................................................................................... 43
Complex slopes on a hillslope of interbedded sedimentary rocks in 
Wildcat Hills, Nebraska.
Figure 2-14 ..................................................................................... 46
Slope shape based on combinations of surface curvature.
Figure 2-15 ..................................................................................... 47
Three-dimensional depiction of geomorphic components of hills.
Figure 2-16 ..................................................................................... 48
Three-dimensional depiction of geomorphic components of terraces 
and stepped landforms.
Figure 2-17 ..................................................................................... 49
Three-dimensional depiction of geomorphic components of 
mountains.
Figure 2-18 ..................................................................................... 50
Three-dimensional depiction of geomorphic components of flat 
plains.
Figure 2-19 ..................................................................................... 51
Water ponding in the microlows in an area of Vertisols that exhibits 
gilgai microfeatures. 
Figure 2-20 ..................................................................................... 51
Illustrations and descriptive terms for drainage patterns. 
Chapter 3.—Examination and Description of Soil 
Profiles
Figure 3-1 ....................................................................................... 89
A shallow soil pit with a face that has been cleaned and prepared 
for describing the soil profile. 
Figure 3-2 ....................................................................................... 90
A horizontal view of a fragipan from a soil in Tennessee. 
Figure 3-3 ....................................................................................... 98
A soil with a permanently frozen ice layer between depths of 60 and 
130 cm. 
Figure 3-4 ..................................................................................... 113
Examples of topography classes for horizon boundaries. 
Figure 3-5 ..................................................................................... 115
Five kinds of near surface subzones. 
Figure 3-6 ..................................................................................... 121
Relationships among particle-size classes of the USDA system and 
four other systems.
 soil survey Manual ix
Figure 3-7 ..................................................................................... 125
USDA textural triangle showing the percentages of clay, silt, and 
sand in the 12 basic texture classes.
Figure 3-8 ..................................................................................... 135
A soil in which the layers below a depth of about 20 cm are very 
cobbly loamy sand. 
Figure 3-9 ..................................................................................... 143
An area of bouldery soil (class 1).
Figure 3-10 ................................................................................... 143
An area of very bouldery soil (class 2).
Figure 3-11 ................................................................................... 144
An area of extremely bouldery soil (class 3).
Figure 3-12 ................................................................................... 144
An area of rubbly soil (class 4).
Figure 3-13 ................................................................................... 145
An area of very rubbly soil (class 5).
Figure 3-14 ................................................................................... 147
The arrangement of color chips according to value and chroma on 
the Munsell soil-color card of hue 10YR. 
Figure 3-15 ................................................................................... 148
A schematic diagram showing relationships among hue, value, and 
chroma in the Munsell color system. 
Figure 3-16 ................................................................................... 157
Examples of soil structure types.
Figure 3-17 ................................................................................... 158
Prismatic soil structure. 
Figure 3-18 ................................................................................... 159
Peds with angular blocky structure. 
Figure 3-19 ................................................................................... 163
Large reversible trans-horizon cracks extending from the soil 
surface deep into the subsoil of a clayey soil. 
Figure 3-20 ................................................................................... 164
Shiny clay films coating the surface of a ped. 
Figure 3-21 ................................................................................... 165
Sand grains coated and bridged with illuvial clay. 
Figure 3-22 ................................................................................... 166
Prominent slickensides in the Bss horizon of a Vertisol.
Figure 3-23 ................................................................................... 169
Masses of secondary calcium carbonate in the calcic horizon of an 
Aridisol.
x lisT of figures
Figure 3-24 ................................................................................... 170
A soil with a reticulately mottled zone with plinthite below a depth 
of about 2 feet.
Figure 3-25 ................................................................................... 171
A cluster of gympsum crystals (selenite) in an Aridisol.
Figure 3-26 ................................................................................... 176
Schematic diagram of diagnostic carbonate morphology for 
the four main stages of carbonate accumulation in two 
morphogenetic sequences. 
Figure 3-27 ................................................................................... 179
Redoximorphic features consisting of a redox concentration as an 
iron mass and an iron depletion. 
Figure 3-28 ................................................................................... 190
A field test on a soil with a moderately fluid manner of failure class. 
Figure 3-29 ................................................................................... 206
Jarosite concentrations that formed due to oxidation in a drained 
marsh soil containing sulfides.
Figure 3-30 ................................................................................... 212
Model-basedcurve for a medium textured horizon and the 
relationship of water state class limits to water contents 
determined from the desorption curve.
Figure 3-31 ................................................................................... 224
Bulk density classes: low, medium, and high. 
Figure 3-32 ................................................................................... 225
Saturated hydraulic conductivity classes based on bulk density and 
texture relationships.
Chapter 4.—Soil Mapping Concepts
Figure 4-1 ..................................................................................... 242
A truck-mounted hydraulic probe. 
Figure 4-2 ..................................................................................... 243
A backhoe excavation and safety measures in deep trenches. 
Figure 4-3 ..................................................................................... 247
Illustration of polypedons. 
Figure 4-4 ..................................................................................... 258
Three images of an area that meets the definition of a soil complex. 
Figure 4-5 ..................................................................................... 259
Block diagram depicting the relationship of the soils in the 
Monona-Ida-Judson association in the general soil map of 
Woodbury County, Iowa. 
Figure 4-6 ..................................................................................... 277
Diagram illustrating soil correlation as a continuous process. 
soil survey Manual xi
Chapter 5.—Digital Soil Mapping
Figure 5-1 ..................................................................................... 306
Comparison of spectral bands of common sensors to the reflectance 
spectra of common materials.
Figure 5-2 ..................................................................................... 320
Flow chart illustrating the general steps in selecting environmental 
covariates.
Figure 5-3 ..................................................................................... 322
Simplistic representation of sampling locations as determined by 
simple random, systematic, stratified random, and multistage 
random sampling designs.
Figure 5-4 ..................................................................................... 324
A comparison of the distribution of simple random, stratified 
random, and cLHS sampling methods over the data range of a 
slope gradient covariate.
Figure 5-5 ..................................................................................... 327
ISODATA unsupervised classification of both terrain and spectral 
data derivatives in eastern Emery County, Utah. 
Figure 5-6 ..................................................................................... 329
Simplistic representation of hard classification and fuzzy 
classification. 
Figure 5-7 ..................................................................................... 330
Supervised fuzzy classification of Landsat imagery for an area 
along the east shore of the Great Salt Lake, Utah. 
Figure 5-8 ..................................................................................... 332
Output from a hierarchical decision-tree knowledge-based 
classification for four classes. 
Figure 5-9 ..................................................................................... 333
Classification using random forests method for parent material 
classes in the Boundary Waters Canoe Area Wilderness, 
Minnesota. 
Figure 5-10 ................................................................................... 336
Interpolation using ordinary kriging of soil K concentration in the 
Salt Lake City Valley, Utah. 
Figure 5-11 ................................................................................... 341
Example of the confusion index for soil class prediction over 
approximately 300 km2 in the Powder River Basin, Wyoming. 
Figure 5-12 ................................................................................... 342
Example of prediction intervals and prediction interval width for 
soil depth to a restricting layer over approximately 50 km2 in 
San Juan County, Utah. 
xii lisT of figures
Figure 5-13 ................................................................................... 343
Example of a disaggregation of SSURGO in West Virginia. 
Chapter 6.—Tools for Proximal Soil Sensing
Figure 6-1 ..................................................................................... 359
A typical GPR system. 
Figure 6-2 ..................................................................................... 360
A radar record showing well expressed spodic and argillic horizons 
in a Pomona soil in north-central Florida.
Figure 6-3 ..................................................................................... 361
A radar record showing a discontinuity separating a loamy eolian 
mantle from sandy glacial outwash in southern Rhode Island.
Figure 6-4 ..................................................................................... 362
A terrain-corrected radar record in which a water table provides a 
high-amplitude reflector in a dune field in Indiana.
Figure 6-5 ..................................................................................... 363
A radar record from an area of Freetown soils showing the 
thickness of organic soil materials that overlie coarse textured 
glacial outwash.
Figure 6-6 ..................................................................................... 367
Three of the commercially available ground conductivity meters 
used in soil investigations. 
Figure 6-7 ..................................................................................... 369
Spatial variations in ECa within the upper 150 cm of the soil 
profiles at a site in northern Texas. 
Figure 6-8 ..................................................................................... 369
Spatial variations in ECa within the upper 150 cm of five soils in 
northern Iowa. 
Figure 6-9 ..................................................................................... 371
Spatial distribution of ECa across a cultivated field in north-central 
Montana. 
Figure 6-10 ................................................................................... 373
A towed electrode-array soil ECa mapping system behind a utility 
vehicle in a field of corn stubble.
Figure 6-11 ................................................................................... 374
Maps of apparent conductivity prepared from shallow and deep 
data collected in west-central Illinois.
Figure 6-12 ................................................................................... 376
A common capacitively induced coupling resistivity system. 
Figure 6-13 ................................................................................... 376
A soil electrical conductivity depth profile from an agricultural test 
plot at Ohio State University. 
soil survey Manual xiii
Figure 6-14 ................................................................................... 377
Magnetic surveying with a cesium vapor gradiometer integrated 
with a global positioning system receiver. 
Figure 6-15 ................................................................................... 380
A portable XRF spectrometer. 
Figure 6-16 ................................................................................... 382
A probe equipped with insertion load sensors and two 
spectrometers. 
Figure 6-17 ................................................................................... 383
A vehicle-mounted passive gamma-ray sensor.
Figure 6-18 ................................................................................... 386
A sampling mechanism for a towed system that simultaneously 
maps soil pH and apparent electrical conductivity.
Chapter 7.—Soil Survey Data Collection, 
Management, and Dissemination
Figure 7-1 .....................................................................................406
Standard pedon description form.
Figure 7-2 ..................................................................................... 413
Conceptual model showing the relationships and degree of 
generalization of data between different map scales and 
products. 
Figure 7-3 ..................................................................................... 416
An illustration of the increased number of users of NRCS’s Web Soil 
Survey application.
Chapter 8.—Interpretations: The Impact of Soil 
Properties on Land Use
Figure 8-1 ..................................................................................... 441
Membership function for slope percent for a limitation style 
interpretation. 
Figure 8-2 ..................................................................................... 443
Graphs representing the three basic suitability styles. 
Figure 8-3 ..................................................................................... 444
Diagram of a hypothetical parent rule for dwellings with 
basements. 
Figure 8-4 ..................................................................................... 476
A soil map showing the distribution of mapping units on the 
landscape and an interpretive map showing limitations for 
local roads and streets.
Figure 8-5 ..................................................................................... 479
Conceptual framework of raster-based soil interpretation.
xiv lisT of figures
Chapter 9.—Assessing Dynamic Soil Properties 
and Soil Change
Figure 9-1 ..................................................................................... 483
Relationship between soil functions and some dynamic soil 
properties. 
Figure 9-2 ..................................................................................... 488
A generalized cross-section of a soil landscape near Olivia, 
Minnesota. 
Figure 9-3 .................................................................................... 491
Documentation from the Georgia Longleaf Pine Dynamic Soil 
Property project. 
Figure 9-4 ..................................................................................... 492
Example of pedon placement for a paired site in Dodge County, 
Nebraska. 
Figure 9-5 ..................................................................................... 493
Example of detailed plot sampling instructions for a rangeland DSP 
project in Utah. 
Figure 9-6 ..................................................................................... 498
Dynamic soil property data in relation to ecological sites, soil 
interpretations, and monitoring data. 
Figure 9-7 ..................................................................................... 500
 Dynamic soil properties of 0–2 cm samples for two DSP projects 
for soil organic carbon measured as total carbon and water 
stable aggregates. 
Chapter 10.—Subaqueous Soil Survey
Figure 10-1 ................................................................................... 508
A pontoon boat used for subaqueous soil sampling. 
Figure 10-2 ................................................................................... 509
Equipment for vibracore sampling. 
Figure 10-3 ................................................................................... 510
A core barrel and core catcher. 
Figure 10-4 ................................................................................... 511
A core from subaqueous sampling. 
Figure 10-5 ................................................................................... 512
Incubation pH for three horizons from a Fluventic Sulfiwassent. 
Figure 10-6 ................................................................................... 514
Examples of subaqueous landscape units across a coastal lagoon.
Figure 10-7 ................................................................................... 515
Soil-landscape relationships across a coastal lagoon in Rhode 
Island and Connecticut.
soil survey Manual xv
Figure 10-8 ................................................................................... 519
GPR output for a freshwater lake with thick organic materials. 
Chapter 11.—Human-Altered and Human- 
Transported Soils
Figure 11-1 ................................................................................... 527
Landfill complex in Virginia. 
Figure 11-2 ................................................................................... 528
Machu Picchu, Peru. 
Figure 11-3 ................................................................................... 529
Profile of the Laguardia soil series showing artifacts in multiple 
deposits of human-transported material. 
Figure 11-4 ................................................................................... 530
An ancient Roman urban anthroscape. 
Figure 11-5 ................................................................................... 533
McMurdo Station, Antarctica. 
Figure 11-6 ................................................................................... 551
A profile of the Ladyliberty soil series. 
Appendix 1.—Official Soil Series Description
Figure A-1 ..................................................................................... 560
Profile of the Olton series.
Appendix 2.—Detailed Map Unit Description
No figures.
Appendix 3.—NCSS Soil Characterization Database
No figures.
Appendix 4.—Web Soil Survey
Figure A-2 ..................................................................................... 574
Soil map showing an area of interest on the Southern High Plains of 
western Texas and eastern New Mexico. 
Figure A-3 ..................................................................................... 574
The map legend and conventional symbols found on soil maps.
Figure A-4 ..................................................................................... 579
Map showing land capability class.
Figure A-5 ..................................................................................... 580
Map showing hydrologic soil groups. 
Figure A-6 ..................................................................................... 581
Map showing ecological sites. 
Figure A-7 ..................................................................................... 582
Shortgrass/blue gramma dominant community of the Deep 
Hardland ecological site (R077CY022TX). 
xvi lisT of figures
Figure A-8 ..................................................................................... 583
State-and-transition model showing pathways and causes of change 
in the plant communities.
xvii
List of Tables
Chapter 1.—Soil and Soil Survey
No tables.
Chapter 2.—Landscapes, Geomorphology, and Site 
Description
Table 2-1 ......................................................................................... 31
Physiographic Location, Relative Scale (in Descending 
Order) and Examples in the U.S.
Table 2-2 ......................................................................................... 35
Prominent Geomorphic Environments and Processes in 
the U.S. and Examples
Table 2-3 ......................................................................................... 44
Definitions of Slope Classes
Table 2-4 ......................................................................................... 47
Geomorphic Component Terms for Hills
Table 2-5 ......................................................................................... 48
Geomorphic Component Terms for Terraces and 
Stepped Landforms
Table 2-6 ......................................................................................... 49
Geomorphic Component Terms for Mountains
Table 2-7 ......................................................................................... 50
Geomorphic Component Terms for Flat Plains
Table 2-8 ......................................................................................... 62
Types of Landslide Deposits 
Table 2-9 .........................................................................................64
General Groups of Parent Materials Based on 
Geomorphic Process or Setting
Table 2-10 ....................................................................................... 69
Lithostratigraphic Units and Their Hierarchical Rank 
and Definition
Table 2-11 ....................................................................................... 71
Kinds of Accelerated Erosion
xviii lisT of Tables
Table 2-12 ....................................................................................... 76
Degree Classes for Accelerated Soil Erosion 
Chapter 3.—Examination and Description of Soil 
Profiles
Table 3-1 ....................................................................................... 126
General Soil Texture Groups
Table 3-2 ....................................................................................... 134
Terms for Rock Fragments and Pararock Fragments
Table 3-3 ....................................................................................... 135
Guide for Determining Rock Fragment Modifier of 
Texture for Soils with a Mixture of Rock Fragment 
Sizes
Table 3-4 ....................................................................................... 142
Classes of Surface Stones and Boulders in Terms of 
Cover and Spacing
Table 3-5 ....................................................................................... 153
Color Contrast Class Terms and Their Criteria
Table 3-6 ....................................................................................... 160
Size Class Terms for Peds with Various Soil Structure 
Types
Table 3-7 ....................................................................................... 183
Rupture Resistance Classes for Blocklike Specimens
Table 3-8 ....................................................................................... 185
Rupture Resistance Classes Applied to Crushing Plate- 
Shaped Specimens
Table 3-9 ....................................................................................... 186
Plasticity Classes
Table 3-10 ..................................................................................... 186
Toughness Classes
Table 3-11 ..................................................................................... 187
Stickiness Classes
Table 3-12 ..................................................................................... 188
Manner of Failure Classes
Table 3-13 ..................................................................................... 191
Penetration Resistance Classes
Table 3-14 ..................................................................................... 192
Excavation Difficulty Classes
 soil survey Manual xix
Table 3-15 ..................................................................................... 199
Reaction Class Terms and Their Ranges in pH
Table 3-16 ..................................................................................... 200
Effervescence Class Terms
Table 3-17 ..................................................................................... 202
Salinity Class Terms
Table 3-18 ..................................................................................... 207
Frequency and Duration of Inundation Classes 
(Flooding or Ponding)
Table 3-19 ..................................................................................... 209
Water State Classes
Table 3-20 ..................................................................................... 215
Classes of Internal Free Water
Table 3-21 ..................................................................................... 216
Example of a Water State Annual Pattern
Table 3-22 ..................................................................................... 221
Classes of Saturated Hydraulic Conductivity 
Table 3-23 ..................................................................................... 222
Saturated Hydraulic Conductivity Class Limits in 
Equivalent Units
Chapter 4.—Soil Mapping Concepts
Table 4-1 ....................................................................................... 250
Kinds of Map Unit Components Used in Soil Survey
Table 4-2 ....................................................................................... 254
Miscellaneous Areas Used as Map Unit Components
Table 4-3 ....................................................................................... 267
Phases Most Commonly Used in Naming Soil Map 
Units
Table 4-4 ....................................................................................... 270
Key for Identifying Orders of Soil Surveys
Table 4-5 ....................................................................................... 281
Major Applications of Soil Survey Standards
Chapter 5.—Digital Soil Mapping
Table 5-1 ....................................................................................... 312
Selected Primary and Compound Terrain Attributes 
Used in Digital Soil Mapping
xx lisT of Tables
Table 5-2 ....................................................................................... 315
Spectral Band Ratios Used in Digital Soil Mapping 
Table 5-3 ....................................................................................... 338
Confusion Matrix of Three Modeled Soil Subgroup 
Classes
Chapter 6.—Tools for Proximal Soil Sensing
Table 6-1 ....................................................................................... 357
Methods of Proximal Soil Sensing and Their Primary 
Application in Soil Survey
Chapter 7.—Soil Survey Data Collection, 
Management, and Dissemination
No tables.
Chapter 8.—Interpretations: The Impact of Soil 
Properties on Land Use
Table 8-1 ....................................................................................... 438
Interpretive Soil Properties and Limitation Classes for 
Septic Tank Absorption Fields
Table 8-2 ....................................................................................... 439
Values of Applicable Interpretive Properties for Septic 
Systems for an Aksarben Component
Table 8-3 ....................................................................................... 477
Limitation Ratings for Local Roads and Streets for the 
Albrights Map Unit (AbB)
Chapter 9.—Assessing Dynamic Soil Properties 
and Soil Change
Table 9-1 ....................................................................................... 493
DSP Project Data Elements Collected at Site (Across 
Plot) Scales
Table 9-2 ....................................................................................... 494
DSP Project Data Elements Collected at Pedons; 
Multiple Locations per Site/Plot
Table 9-3 ....................................................................................... 496
Measurements of Dynamic Soil Properties on 
Individual Samples
Chapter 10.—Subaqueous Soil Survey
No tables.
soil survey Manual xxi
Chapter 11.—Human-Altered and Human- 
Transported Soils
Table 11-1 ..................................................................................... 543
Soil Taxonomy Subgroups and HAHT Soil Concepts
Table 11-2 ..................................................................................... 544
Soil Taxonomy Family Terms and HAHT Soil 
Concepts
Appendix 1.—Official Soil Series Description
No tables.
Appendix 2.—Detailed Map Unit Description
No tables.
Appendix 3.—NCSS Soil Characterization 
Database
Table A-1 ...................................................................................... 564
Primary Characterization Data
Table A-2 ...................................................................................... 570
Supplementary Characterization Data
Appendix 4.—Web Soil Survey
Table A-3 ...................................................................................... 575
Map Unit Symbols and Names Displayed on the Soil 
Map for the Area of Interest
Table A-4 ...................................................................................... 576
Aggregation MethodsTable A-5 ...................................................................................... 584
Engineering Properties and Classifications
Table A-6 ...................................................................................... 585
Soil Chemical Properties
xxiii
Introduction to the Fourth Edition
By Craig Ditzler, Kenneth Scheffe, and H. Curtis Monger, 
USDA–NRCS.
The Soil Survey Manual, USDA Handbook No. 18, provides the 
major principles and practices needed for making and using soil surveys 
and for assembling and using related data. The term “soil survey” is used 
here to encompass the process of mapping, describing, classifying, and 
interpreting natural three-dimensional bodies of soil on the landscape. 
This work is performed by the National Cooperative Soil Survey in the 
United States and by other similar organizations worldwide. The Manual 
provides guidance, methodology, and terminology for conducting a 
soil survey but does not necessarily convey policies and protocols 
required to administer soil survey operations. The soil bodies contain 
a sequence of identifiable horizons and layers that occur in repeating 
patterns in the landscape as a result of the factors of soil formation as 
described by Dokuchaev (1883) and Jenny (1941). Soil scientists gain 
an understanding of the factors of soil formation in their area, along with 
the resulting expression of their interaction in the soil, and are then able 
to make maps of the natural soil bodies quite efficiently (Hudson, 1992). 
The maps of soil bodies are related to, but different from, maps of single 
soil properties, such as organic matter or pH. The latter are made by 
sampling and statistical modeling to show how these properties vary over 
the landscape.
Purpose
The Manual is intended primarily for use by soil scientists engaged 
in the work of making soil surveys. It is an especially important reference 
for soil scientists early in their careers as they learn the many complex 
aspects of making a soil survey. It is also an important reference for 
experienced soil surveyors who want to review the details regarding 
many of the standards used in soil survey. For example, chapter 3, 
“Examination and Description of Soil Profiles,” contains the accepted 
xxiv inTroduCTion
terms and definitions for specific soil properties that are used when 
describing soil profiles in the field. It also contains extensive information 
describing each soil property and the proper procedures for observing 
or measuring it in the field. The Manual is therefore an important 
companion to other soil survey references, such as the National Soil 
Survey Handbook (USDA-NRCS, 2016), the Field Book for Describing 
and Sampling Soils (Schoeneberger and Wysocki, 2012), and the Keys to 
Soil Taxonomy (Soil Survey Staff, 2014).
Although the Manual is oriented to the needs of those actively 
engaged in preparing soil surveys, workers and students who have limited 
soil science experience or are less familiar with the soil survey process 
can also use the information. Teachers, researchers, and students of soil 
science and related disciplines, especially those interested in pedology, 
soil morphology, soil geography, ecology, geomorphology, and the 
science underlying soil survey, will find this manual useful. Resource 
specialists, such as wetland scientists, foresters, and agronomists, and 
others who use soil surveys in their work, can refer to the Manual to 
better understand how soil surveys are made and how to interpret the 
technical information they provide. Parts of the Manual, especially those 
concerning the description of soils in the field and the soil properties 
considered when predicting soil behavior under a specific use, have 
been adopted by private-sector soil scientists as standards. The Soil 
Survey Manual has proven to be an important source of information for 
government agencies, nongovernmental organizations, and private-sector 
resource specialists in other countries involved in soil survey projects. 
Because the Manual describes all facets of the soil survey process, it is 
an important guide for developing proposals to conduct soil surveys and 
to create detailed plans for projects in other parts of the world.
The Manual serves as the guiding document for activities of the 
National Cooperative Soil Survey (NCSS), a cooperative undertaking led 
by the United States Department of Agriculture. The NCSS includes other 
Federal and State agencies, universities, non-governmental organizations, 
and private-sector soil scientists interested in making soil surveys and/
or interpreting and using soil survey information. The original Federal 
authority for the Soil Survey of the United States is contained in the 
record of the 53rd Congress, Chapter 169, Agricultural Appropriations 
Act of 1896. The authority was elaborated in Public Law 74-46, the Soil 
Conservation Act of April 27, 1936, and again in Public Law 89-560, Soil 
Surveys for Resource Planning and Development, September 7, 1966. 
The Manual is the primary reference on the principles and technical 
details used by the local, State, and Federal contributors to soil surveys 
authorized under these acts.
soil survey Manual xxv
Need for Additions and Revisions
Since the third edition (1993) of the Manual was printed, significant 
changes have occurred that affect the ways soil surveys are made. In 
the United States, greater emphasis is now placed on the maintenance 
and modernization of previously completed soil surveys. Because of this, 
some soil scientists are now evaluating and improving existing surveys 
rather than making new soil surveys. The wide application of computer 
technology, in both the office and the field, has led to a proliferation 
of electronic data sources, including digital elevation models (DEMs), 
Light Detection and Ranging (LiDAR), digital geology maps and 
vegetation maps, and multi-spectral remote sensing data. The electronic 
data sources, combined with computer models that capture and apply 
knowledge of the interaction of the soil-forming factors, have allowed 
soil scientists to partially, and in a few cases totally, automate the soil 
mapping process. This has had an important impact on the scientist’s 
ability to formalize and document the soil-landscape models used to 
produce soil survey maps. It has also led to improved consistency in 
the maps produced using these methods. In addition, tools used for 
proximal sensing of soil properties, such as ground-penetrating radar and 
electromagnetic induction, have been increasingly used in special soil 
survey field studies. Greater attention is also being given to recognizing 
anthropogenic influences on soils. This has resulted in a need for the 
development of new standards for horizon nomenclature for human-
altered soils, new terminology for describing human-made materials 
(artifacts) in soil profiles, and new classification groups. Soil surveys 
have also been conducted to a greater extent in shallow water (subaquatic) 
environments. New field procedures, descriptive terms, and taxonomic 
classes have been developed for conducting this innovative work.
Because of these changes, a major revision of the Manual was 
considered essential. Many parts have been revised, some parts have 
been extensively rewritten, and some new sections have been added. 
Entirely new subject matter in this edition of the Soil Survey Manual 
includes:
• Chapter 5, “Digital Soil Mapping.” This chapter presents many
concepts and principles that have been developed regarding the
use of computers and digital technology to aid in the making of
soil surveys.
• Chapter 6, “Tools for Proximal Soil Sensing.” This chapter
covers recent advances in the use of noninvasive tools for rapidly
collecting information about soil properties.
xxvi inTroduCTion
• Chapter 9, “Assessing Dynamic Soil Properties and Soil Change.”
This chapter provides important information for documenting
key soil properties,particularly in the near surface layers that are
significantly impacted by soil management practices.
• Chapter 10, “Subaqueous Soil Survey.” This chapter covers the
emerging specialized field of making soil surveys in shallow
water environments. This work is proving to be highly valuable to
resource managers, especially in coastal estuarine environments.
• Chapter 11, “Human-Altered and Human-Transported Soils.”
This chapter provides valuable guidance on making soil surveys
in environments heavily impacted by humans. Examples include
urban areas, mined sites, and drastically changed soils used for
agriculture.
• Appendices. The new appendices reflect the current form and
content of web-accessible soil survey information in the United
States. They are cross referenced in various places throughout
the text.
Other significant revisions include:
• The former chapter 3 (“Examination and Description of Soils”) is
now split into two chapters: “Landscapes, Geomorphology, and
Site Description” (chapter 2) and “Examination and Description
of Soil Profiles” (chapter 3). This effectively separates the
details for describing landscapes, geomorphology, and local
site characteristics from the details for describing individual
soil profiles. Both chapters incorporate all of the changes and
additions to standard technical terms and their definitions that
have been adopted by the National Cooperative Soil Survey
since the previous publication of the Manual.
• The former chapters 2 (“Soil Systematics”) and 4 (“Mapping
Techniques”) are combined and revised into a new chapter 4,
“Soil Mapping Concepts.” Information in the previous edition
on procedures that have since become obsolete or nearly so (such
as the use of stereoscopes and aerial photo pairs to visualize
landforms in three dimensions, “color checking” to manually
inspect maps for proper joining of units, and use of dot-grids to
determine the aerial extent of map units) has been omitted.
• The former chapters 5 (“Information Recording and Manage-
ment”) and 7 (“Disseminating Soil Survey Information”)
are revised and updated into the new chapter 7, “Soil Survey
Data Collection, Management, and Dissemination.” The new
chapter discusses the use of computer databases to effectively
soil survey Manual xxvii
store and manage soil survey information as well as provide 
information to end users. It also includes a historical summary 
of the development of the National Soil Information System 
(NASIS) in the United States. The summary may be useful to 
those outside the U.S. who are considering the development of a 
similar database.
• The former chapter 6 (“Interpretations”) is revised and updated
into the new chapter 8 (“Interpretations: The Impact of Soil
Properties on Land Use”). The new chapter describes some
of the latest strategies for making current interpretations
more quantitative and providing interpretive information for
anticipated uses.
Online Access
Given the rapid pace of technological change, flexibility is needed 
to provide information in a timely manner. In addition to a bound, hard-
copy version of the Soil Survey Manual, a web-based version is also 
provided. The electronic version has convenient access and distribution 
of the information, and it affords users the option to “print on demand” 
individual parts or the entire document. The user can view each section 
of the Manual as a stand-alone chapter or view the entire document. The 
sections are arranged to correspond to the approximate chronological 
order of the work required to complete a soil survey. The reader has 
the choice of focusing on individual parts of interest or exploring the 
larger picture of conducting a soil survey project from beginning to 
end. Additional supplementary information not provided in the printed 
version will be included with the electronic version.
Citation and Authorship
The previous edition of the Soil Survey Manual (Soil Survey Division 
Staff, 1993) simply listed the author as the Soil Survey Division Staff. The 
contents of the Manual represented the collective contributions of many 
people over several decades. The new edition continues to recognize the 
innumerable past contributors by including the Soil Science Divison Staff 
as an author for chapters that retain significant portions of the previous 
publication. These chapters contain information that has been used for 
decades as well as new information related to improved methods and/
or new terminology. For the updated chapters, authors responsible for 
xxviii inTroduCTion
revisions are listed in addition to the Soil Science Division Staff. For 
entirely new chapters, only individual contributing authors are cited by 
name. Technical content of the Manual was revised and edited by Craig 
Ditzler, Kenneth Scheffe, and H. Curtis Monger. English content was 
revised and edited by Jennifer Sutherland and Aaron Achen.
Recommended Citations
For individual chapters, provide authors and chapter title. For 
example:
Adamchuk, V.I., B. Allred, J. Doolittle, K. Grote, and R.A. Viscarra 
Rossel. 2017. Tools for proximal soil sensing. In C. Ditzler, K. Scheffe, 
and H.C. Monger (eds.) Soil survey manual, USDA Handbook 18, 
Government Printing Office, Washington, D.C., pp. 355–394. 
For the complete manual:
Soil Science Division Staff. 2017. Soil survey manual. C. Ditzler, K. 
Scheffe, and H.C. Monger (eds.). USDA Handbook 18. Government 
Printing Office, Washington, D.C.
Acknowledgements
The following individuals provided valuable assistance in the 
development and review of this edition of the Manual: Tim Warner, West 
Virginia University; Colby Brungard, New Mexico State University; 
Katey Yoast, USDA Food and Nutrition Service; Christopher Dorian, 
private consultant; and Natural Resource Conservation Service employees 
W. Dwain Daniels, Tony Jenkins, Dylan Beaudette, Julie Baker, Tammy
Umholtz, Robert Long, Thomas D’Avello, Travis Nauman, Jessica
Philippe, and Stephen Roecker.
References
Dokuchaev, V.V 1883. Russian chernozem. (Translated from Russian 
by N. Kaner, 1967.) Available from U.S. Department of Commerce, 
Clearinghouse for Federal Scientific and Technical Information, 
Springfield, VA.
Hudson, B.D. 1992. The soil survey as a paradigm-based science. Soil 
Science Society of America Journal 56:836-841.
 soil survey Manual xxix
Jenny, Hans. 1941. Factors of soil formation: A system of quantitative 
pedology. McGraw Hill Book Company, New York, NY.
Schoeneberger, P.J., and D.A. Wysocki. 2012. Geomorphic Description 
System, version 4.2. USDA Natural Resources Conservation Service, 
National Soil Survey Center, Lincoln, NE.
Soil Survey Division Staff. 1993. Soil survey manual. U.S. Department of 
Agriculture Handbook 18. Natural Resources Conservation Service.
Soil Survey Staff. 2014. Keys to soil taxonomy, 12th edition. USDA 
Natural Resources Conservation Service.
U.S. Department of Agriculture, Natural Resources Conservation Service. 
National soil survey handbook, title 430-VI. http://www.nrcs.
usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054242 
[Accessed 22 August 2016]
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054242
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054242
Chapter 
1
Soil and Soil Survey
By Soil Science Division Staff. Revised by Craig Ditzler and 
Larry West, USDA-NRCS.
This chapter describes the term “soil survey” within the context of the National Cooperative Soil Survey (NCSS) in the United States. It discusses the development of pedology and the important 
concept of soils as natural three-dimensional bodies that form as a result 
of the interaction of five soil-forming factors. The repeating patterns 
formed by these natural bodies of soil in the landscape allow soil 
scientists to develop predictive soil-landscape models, which serve as 
the scientific foundation for making soil surveys. Important milestones 
in the development of the Soil Survey in the UnitedStates are discussed 
at the end of this chapter. 
Soil Survey—Definition and Description
A soil survey describes the characteristics of the soils in a given area, 
classifies the soils according to a standard system of taxonomy, plots 
the boundaries of the soils on a map, stores soil property information in 
an organized database, and makes predictions about the suitability and 
limitations of each soil for multiple uses as well as their likely response 
to management systems. The information collected in a soil survey helps 
in the development of land use plans and can be used to evaluate and 
predict the effects of land use on the environment.
A soil map consists of many individual delineations showing the 
location and extent of different soils. The collection of all delineations 
that have the same symbol on the map (e.g., 34B) are a “map unit.” Each 
map unit is named for one or more soils or nonsoil areas (e.g., Sharpsburg 
silt loam). Each kind of soil or nonsoil (e.g., Rock outcrop) making up 
the composition of a map unit is a map unit component. See chapter 4 for 
a full discussion of map units and their components. 
2 ChapTer 1
The soils are natural three-dimensional bodies occupying a 
characteristic part of the landscape. Soil survey maps are therefore 
different from other maps that show just one or a few specific soil 
properties or other environmental information. The concept of soil survey 
as defined for the NCSS is related to, but does not include, maps showing 
the distribution of a single soil property (such as texture, slope, or depth) 
alone or in limited combinations; maps showing the distribution of soil 
qualities (such as productivity or erodibility); and maps of soil-forming 
factors (such as climate, topography, vegetation, or geologic material). 
A soil map from a soil survey, as defined here, delineates areas occupied 
by different kinds of soil, each of which has a unique set of interrelated 
properties characteristic of the material from which it formed, its 
environment, and its pedogenic history. The soils mapped by the NCSS 
are identified by names that serve as references to a national system of 
soil classification.
The geographic distribution of many individual soil properties or soil 
qualities can be extracted from soil maps and shown on separate maps for 
special purposes, such as showing predicted soil behavior for a particular 
use. Numerous interpretative maps can be derived from a soil map, and 
each of these maps would differ from the others according to its purpose. 
A map made for one specific interpretation rarely can serve a different 
purpose.
Maps that show one or more soil properties can be made directly 
from field observations without making a basic soil map. Such maps 
serve their specific purposes but have few other applications. Predictions 
of soil behavior can also be mapped directly; however, most of these 
interpretations will need to be changed with changes in land use and in 
the cultural and economic environment. For example, a map showing the 
productivity of crops on soils that are wet and undrained has little value 
after drainage systems have been installed. If the basic soil map is made 
accurately, and a wide array of soil property data is collected and stored 
in an organized database, interpretative maps can be revised as needed 
without additional fieldwork. In planning soil surveys, this point needs 
to be emphasized. In some cases, inventories are made for some narrow 
objective, perhaps at a cost lower than that of a soil survey. Generally, 
maps for these inventories quickly become obsolete. They cannot be 
revised without fieldwork because vital data are missing, facts are mixed 
with interpretations, or boundaries between significantly different soil 
units have been omitted.
The basic objective of soil surveys is the same for all kinds of land, 
but the number of map units, their composition, and the detail of mapping 
vary with the complexity of the soil patterns and the specific needs 
soil survey Manual 3
of the users. Thus, a soil survey is designed for the soils and the soil-
related problems of the area. Soil surveys increase general knowledge 
about soils and serve practical purposes. They provide soil information 
about specific geographic areas needed for regional or local land use 
plans. These plans include resource conservation for farms and ranches, 
development of reclamation projects, forest management, engineering 
projects, as well as other purposes.
Early Concepts of Soil
One of the earliest scholars of soils in the United States was Edmund 
Ruffin of Virginia. He worked diligently to find the secret of liming and 
discovered what is now called exchangeable calcium. After writing a brief 
essay in the American Farmer in 1822, he published the first edition of 
An Essay on Calcareous Manures in 1832. Much of what Ruffin learned 
about soils had to be rediscovered because his writings were circulated 
only in the South.
E.W. Hilgard was one of the first modern pedologists in the United 
States. His early concepts of soil (Hilgard, 1860, 1884, 1906) were 
based on ideas developed by the German chemist Justus von Liebig 
and modified and refined by agricultural scientists who worked on soil 
samples in laboratories, in greenhouses, and on small field plots. Soils 
were rarely examined below the depth of normal tillage. The chemists 
had a “balance-sheet” theory of plant nutrition. Soil was considered a 
more or less static storage bin for plant nutrients—the soils could be 
used and replaced. This concept still has value when applied within the 
framework of modern soil science, although a useful understanding of 
soils goes beyond the removal of nutrients from soil by harvested crops 
and their return to soil through manure, lime, and fertilizer.
Early geologists generally accepted the balance-sheet theory of soil 
fertility and applied it within the framework of their own discipline. They 
described soil as disintegrated rock of various sorts—granite, sandstone, 
glacial till, etc. However, they also described how the weathering 
processes modified this material and how geologic processes shaped it 
into landforms (such as glacial moraines, alluvial plains, loess plains, 
and marine terraces). N.S. Shaler’s monograph on the origin and nature 
of soils summarized the late 19th century geological concept of soils 
(Shaler, 1891). Other details were added by G.P. Merrill (1906).
Near the end of the 19th century, Professor Milton Whitney 
inaugurated the National Soil Survey Program (Jenny, 1961). In the 
newly organized soil research unit of the U.S. Department of Agriculture, 
4 ChapTer 1
Whitney and his coworkers discovered great variations among natural 
soils—persistent variations that were in no way related to the effects of 
agricultural use. They emphasized the importance of soil texture and the 
capacity of the soil to furnish plants with moisture as well as nutrients. 
About this time, Professor F.H. King of the University of Wisconsin also 
reported the importance of the physical properties of soils (King, 1910).
Early soil surveys were made to help farmers locate soils responsive 
to different management practices and to help them decide what crops 
and management practices were most suitable for the particular kinds 
of soil on their farms. Many who worked on these early surveys were 
geologists because only geologists were skilled in the field methods and 
scientific correlation needed for the study of soils. They thought of soils 
as mainly the weathering products of geologic formations, defined by 
landform and lithologic composition. Most of the soil surveys published 
before 1910 were strongly influenced by these concepts. Those published 
from 1910 to 1920 were further refined and recognized more soil features 
but retained fundamentally geological concepts.
Early field workers soon learned that many important soil properties 
were not necessarily related toeither landform or kind of rock. They 
noted that soils with poor natural drainage had different properties than 
soils with good natural drainage and that many sloping soils were unlike 
level ones. Topography was clearly related to soil profile differences. 
Soil structure was described in soil survey as early as 1902, in the soil 
survey of the Dubuque Area, Iowa (Fippin, 1902). The 1904 soil survey 
of Tama County, Iowa (Ely et. al., 1904) reported that soils that had 
formed under forest contrasted markedly with other soils that had similar 
parent material but formed under grass.
Soils as Natural Bodies
The balance-sheet theory of plant nutrition dominated laboratory 
work, while the geological concept dominated fieldwork. Both approaches 
were taught in many classrooms until the late 1920s. Although broader 
and more generally useful concepts of soil were being developed by some 
soil scientists, especially Hilgard (1860) and Coffey (1912) in the U.S. 
and soil scientists in Russia, the necessary data for formulating these 
broader concepts came from the fieldwork of the Soil Survey during the 
first decade of its operations in the United States. The concept of the solum 
and the A-B-C horizon nomenclature were becoming central to pedology 
and soil survey (Tandarich et al., 2002). After the work of Hilgard, the 
most significant advance toward a more satisfactory concept of soil was 
made by G.N. Coffey. Coffey determined that the ideal classification of 
soil survey Manual 5
soil was a hierarchical system based on the unique characteristics of soil 
as “a natural body having a definite genesis and distinct nature of its own 
and occupying an independent position in the formations constituting the 
surface of the earth” (Cline, 1977).
Beginning in 1870, the Russian school of soil science under the 
leadership of V.V. Dokuchaev and N.M. Sibertsev was developing a new 
concept of soil. The Russian scientists conceived of soils as independent 
natural bodies, each with unique properties resulting from a unique 
combination of climate, living matter, parent material, relief, and time 
(Gedroiz, 1925). They hypothesized that properties of each soil reflected 
the combined effects of the particular set of genetic factors responsible 
for the soil’s formation, emphasizing the importance of the “zonal” 
concept (i.e., the bioclimatic zone in which the soil formed). Hans Jenny 
later emphasized the functional relationships between soil properties and 
soil formation. The results of this work became generally available to 
Americans through the publication in 1914 of K.D. Glinka’s textbook 
in German and especially through its translation into English by C.F. 
Marbut in 1927 (Glinka, 1927).
The Russian concepts were revolutionary. Soil properties were no 
longer based wholly on inferences from the nature of rocks or from 
climate or other environmental factors, considered singly or collectively. 
Instead, the integrated expression of all these factors could be seen in the 
morphology of the soils. This concept required that all properties of soils 
be considered collectively in terms of a completely integrated natural 
body. In short, it made possible a science of soil.
As a result of the early enthusiasm for the new concept and for the 
rising new discipline of soil science, some suggested that the study of soil 
could proceed without regard to the older concepts derived from geology 
and agricultural chemistry. Certainly, the reverse was true. Besides laying 
the foundation for a soil science with its own principles, the new concept 
made the other sciences even more useful. Soil morphology provides a 
firm basis on which to group the results of observation, experiments, and 
practical experience and to develop integrated principles that predict the 
behavior of soils.
Under the leadership of C.F. Marbut, the Russian concept was 
broadened and adapted to conditions in the United States (Marbut, 1921). 
As mentioned earlier, this concept emphasized individual soil profiles and 
subordinated external soil features and surface geology. By emphasizing 
soil profiles, however, soil scientists initially tended to overlook the 
natural variability of soils, which can be significant even within a small 
area. Overlooking the variability of soils seriously reduced the value 
of maps that showed the location of soils. This weakness soon became 
6 ChapTer 1
evident in the U.S., perhaps because of the emphasis on making detailed 
soil maps for their practical, predictive value. Progress in transforming 
the profile concept into a more reliable predictive tool was rapid because 
a large body of important field data had already been accumulated. By 
1925, a large amount of morphological and chemical work was being 
done on soils throughout the country. The data collected by 1930 were 
summarized and interpreted in accordance with this concept, as viewed 
by Marbut in his work on the soils of the United States (Marbut, 1935).
Early emphasis on genetic soil profiles was so great as to suggest that 
material lacking a genetic profile, such as recent alluvium, was not soil. A 
sharp distinction was drawn between rock weathering and soil formation. 
Although a distinction between these sets of processes is useful for some 
purposes, rock and mineral weathering and soil formation commonly are 
indistinguishable.
The concept of soil was gradually broadened and extended during the 
years following 1930, essentially through consolidation and balance. The 
major emphasis had been on the soil profile. After 1930, morphological 
studies were extended from single pits to long trenches or a series of 
pits in an area of a soil. The morphology of a soil came to be described 
by ranges of properties deviating from a central concept instead of by a 
single “typical” profile. The development of techniques for mineralogical 
studies of clays also emphasized the need for laboratory studies.
The clarification and broadening of soil science also was due to 
the increasing emphasis on detailed soil mapping. Concepts changed 
with increased emphasis on predicting crop yields for each kind of soil 
shown on the maps. Many of the older descriptions of soils had not 
been quantitative enough and the units of classification had been too 
heterogeneous to use in making the yield and management predictions 
needed for planning the management of individual farms or fields.
During the 1930s, soil formation was explained in terms of loosely 
conceived processes, such as “podzolization,” “laterization,” and 
“calcification.” These were presumed to be unique processes responsible 
for the observed common properties of the soils of a region (Jenny, 1946).
In 1941, Hans Jenny’s Factors of Soil Formation: A System of 
Quantitative Pedology concisely summarized and illustrated many of the 
basic principles of modern soil science to that date (Jenny, 1941). Since 
1940, time has assumed much greater significance among the factors of 
soil formation and geomorphological studies have become important in 
determining the time that soil material at any place has been subjected 
to soil-forming processes. Meanwhile, advances in soil chemistry, soil 
physics, soil mineralogy, and soil biology, as well as in the basic sciences 
that underlie them, have added new tools and new dimensions to the 
 soil survey Manual 7
study of soil formation. As a consequence, the formation of soil has come 
to be treated as the aggregate of many interrelated physical, chemical, 
and biological processes. These processes are subject to quantitative 
study in soil physics, soil chemistry, soil mineralogy, and soil biology. 
The focus also has shifted from the study of gross attributes of the whole 
soil to the co-varying detail of individual parts, including grain-to-grain 
relationships.
Early Development of Soil Classification
C.F. Marbut strongly emphasized that the classification of soils should 
be based on morphology instead of on theories of